The present invention relates to turbine buckets having an airfoil and a tip shroud carried by the airfoil. More particularly, the invention relates to leading, trailing and Z-form edge profiles of a tip shroud carried by an airfoil of a turbine bucket.
Buckets for turbines typically comprise an airfoil, a platform, a shank and dovetail. The dovetail is secured in a complementary slot in a turbine wheel. Oftentimes, the airfoil includes an integrally formed tip shroud. The bucket including the airfoil and tip shroud are, of course, rotatable about the engine centerline during operation and the airfoil and the tip shroud are located in the hot gas path. Because the tip shroud is mounted at the tip of the airfoil, substantial stresses occur in the tip shroud fillet region between the tip shroud and the airfoil tip. Particularly, a significant difference in fillet stresses occurs between pressure and suction sides of the airfoil at its intersection with the tip shroud because of tip shroud mass imbalance relative to the airfoil. This mass imbalance negatively impacts the creep life of the bucket. That is, the tip shroud mass distribution in prior buckets resulted in a highly loaded tip shroud fillet and reduced creep life. Further, certain prior tip shrouds do not cover the airfoil throat, with resultant negative impact on stage efficiency due to flow leakage over the tip shroud.